Higher maternal risk of DS has been observed in the presence of this polymorphism, in combination with other genetic polymorphisms relating to folate metabolism, such as MTHFR C677T, MTHFR A1298C and MTR A2756G.9,10 This may be due to the small impact of RFC1 A80G polymorphism on the affinity and transport efficiency of the variant enzyme in relation to the wild-type enzyme.31 Here, MTR is linked to Dravet syndrome.